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Middleware

Middleware functions run on the HTML string before it is parsed into DocumentElement nodes. They allow you to transform, sanitize, or minify the HTML content.

Signature​

import { Middleware } from 'html-to-document';

type Middleware = (html: string) => Promise<string>;

See the Types Reference for the full definition.

Default Middleware​

By default, init() applies a built-in whitespace-minifying middleware (unless you set clearMiddleware: true). This default middleware:

  • Strips HTML comments (<!-- ... -->)
  • Collapses consecutive whitespace into a single space (outside <pre>)
  • Removes unnecessary whitespace between tags
  • Trims leading and trailing whitespace

Custom Middleware​

There are two ways to register your own middleware:

1. Via init options​

import { init } from 'html-to-document';

// Example: remove all <script> tags
const stripScripts: Middleware = async (html) =>
  html.replace(/<script[\s\S]*?>[\s\S]*?<\/script>/g, '');

const converter = init({
  clearMiddleware: true,    // skip default minifier
  middleware: [stripScripts],
});

2. Programmatically​

const converter = init();
// Add another middleware after initialization
converter.useMiddleware(stripScripts);

Note: Middleware functions are executed in the order they are passed in or registered. Make sure to arrange them accordingly if one depends on the output of another.

Example: Sanitizing HTML​

import { init } from 'html-to-document';

// Remove all inline styles
const removeStyles: Middleware = async (html) =>
  html.replace(/ style="[^"]*"/g, '');

const converter = init({
  middleware: [removeStyles],
});

converter.convert('<p style="color:red">Hello</p>', 'docx')
  .then(buffer => /* ... */)
  .catch(console.error);